Prior art cellular-type wireless communication systems, such as universal mobile telecommunication services (UMTS) systems, comprise a plurality of cells having a particular coverage area. As a wireless transmit/receive unit (WTRU) moves across the boundary of the cells, the WTRU needs to handover from one cell to another.
Each cell broadcasts information necessary to facilitate the handover procedure within the UMTS system. This information typically includes a neighbor cell list comprising a list of neighbor cells in the vicinity of the serving cell. The neighbor cell list enables a WTRU to search through only a limited number of cells, instead of all possible codes. As a result, the WTRU is able to speed up the cell search procedure and execute handover to a new cell more quickly.
Meanwhile, wireless local area networks (WLANs) based on IEEE 802.11 standards have been developed, and are widely being deployed. These systems are desirable for their support of high data rate transmissions. One example of the deployment of a WLAN in accordance with 802.11 standards is the use of access points, so called “hot spots”, in public spaces. A WTRU with an 802.11 interface may connect to a hot spot without any physical connections. Once the WTRU is wirelessly associated with the hot spot via RF interface, the WTRU is able to transmit and receive data through the hot spot typically at a much faster data rate than that provided in a UMTS system.
While a hot spot provides high quality, high data rate connectivity, the service range of the hot spot is typically limited to a relatively short range. Since the transmission power of a WTRU under the 802.11 standards is limited to a relatively low power level, it is difficult to achieve sufficient coverage throughout an area of large population. In addition, due to the limited range of 802.11 devices, WTRUs typically perform a constant search procedure for new hot spots. This is a severe processing load and, therefore, a constant drain on WTRUs batteries. In the absence of a mechanism for informing an existence of the hot spot, the WTRU should search signals transmitted from the hot spot periodically and continuously. This causes an unnecessary consumption of processing power and resources.
It would be desirable to provide a dual-mode WTRU which is configured to communicate in, and handover between, a UMTS system and a WLAN system under 802.11 standards, since a WTRU may receive much higher rate services from the hot spot while maintaining a connection in a wide coverage area in a UMTS system. However, currently, there is no convenient method for handover from a cellular-type communication system, such as UMTS, to a wireless local area network (WLAN)-type communication system, such as a hot spot. Therefore, it is desirable to provide a method and system for facilitating inter-system handover between two wireless communication systems, such as UMTS and WLAN.